I have a pair of Haltron EL-34 tubes. I've had them for a long time and can't even remember where I got them.

I had not looked at them in some time and looking a them now, something seems strange about one of them. It appears as if there is no silver coating inside the top of the tube. Just a bit of white.

Here's a picture of the two tubes:

Before I go ahead and plug these in to my amp, can anyone tell me if the one on the left is damaged or faulty in any way? Or is the lack of the silver coating not something I should be concerned about?

Also, I've read that Haltron would rebrand tubes made by other manufacturers. Can anyone tell if this is the case with these tubes? Here's a picture of the bottom if that helps. I read that the hole in the guide pin could indicate that they are from the early 60s. MaybeTeslas?

I'm no expert, but the tube on the left appears to be losing its vacuum. The grey/black material is called getter flash, a characteristic of when the tube is made. When they lose their vacuum, usually due to a crack, that area clears up and turns white eventually.

Someone else will chime in here, but I have a bad feeling that one is shot.

I was afraid the tube was toast since every tube I've ever seen had the silver inside.

I'm slowly educating myself about tubes and have been doing some reading. But there's one thing I'm wondering about and can't find an answer to. Here it is:

I had two pairs of spare tubes. The Haltron pictured above, one of which I now know is toast. The other spare set was a set of Marshall branded tubes. But I dropped one while moving some stuff around the other day and broke it. So that now leaves me with one of the Haltron and one of the Marshall.

In the reading I've done it always mentions matched tube pairs. So my question is, even though they would not be a matched pair (more than likely not even the same brand), could I use the two spare tubes I have (Haltron and Marshall) together in the amp? Or is it a bad idea to mix tubes? Would they even work together if they are too "unmatched"?